This invention relates to a method for selectively removing H.sub.2 S and lower alkyl mercaptans from gaseous streams. More particularly, it relates to a method whereby these sulfur compounds are selectively removed by contacting the gas stream with a liquid piperazinone compound.
Gas streams consisting largely of methane, other lower aliphatic hydrocarbons, hydrogen, and other gases such as natural gas, refinery gases, and coal gasification product streams typically contain acidic contaminants such as H.sub.2 S, lower alkyl mercaptans, other sulfur compounds, and CO.sub.2. It is desirable to separate the H.sub.2 S and any mercaptans that may be present while leaving the CO.sub.2 largely in the gas stream so as to obtain a stream of high H.sub.2 S content for efficient sulfur recovery in a Claus plant or other such sulfur recovery process. Known sour gas purification solvents include ethanolamine, N-methyldiethanolamine, diethanolamine, triethanolamine, isopropanolamine, diisopropanolamine, sulfolane, N-methyl-3-morpholinone, their aqueous solutions, and mixtures of these. While these are effective absorbents for H.sub.2 S, they typically show only kinetic selectivity. Substantial quantities of CO.sub.2 will also be absorbed when it is present.